Multi-rate transmission system

ABSTRACT

A multi-rate transmission system (10) includes a receive section (12) and a transmit section (14). The receive section includes a receiver (16), a clock recovery unit (18), and a serial to parallel converter (20) all operating at a first clock rate (M). The receiver (16) also has a frame recovery unit (22) that operates at any of a plurality of clock rates, including the first clock rate (M) and a second clock rate (M/n). When the frame recovery unit operates at the first clock rate (M), frame information received by the receiver section (12) has unique bits occupying each bit position associated with each clock pulse of the first clock rate (M). When the frame recovery unit (22) operates at the second clock rate (M/n), each unique bit of the frame information occupies a number of bit positions according to a ratio of the first clock rate (M) to the second clock rate (M/n). Similar operation occurs with respect to a frame formatter (30) in the transmit section (14) of the multi-rate transmission system (10).

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to a telecommunicationsenvironment and more particularly to a multi-rate transmission system.

BACKGROUND OF THE INVENTION

Many modern transmission products, such as SONET fiber optictransmission systems, are required to have variants in order to operateat different clock rates. Development of these products becomesunnecessarily complicated and time consuming because one set ofcomponents is required for one clock rate and another set of componentsis required for another clock rate. Upgrading the transmission system orchanging the clock rate requires disposal and replacement of a largenumber of components, significantly increasing the cost and design cycletime of the system. Further, changes in system clock rates cannot beperformed remotely, requiring the system to suffer down time in order toaffect the changes. Therefore, it is desirable to have a transmissionsystem that can perform in response to changes in clock rates withoutadversely affecting performance and development.

SUMMARY OF THE INVENTION

From the foregoing, it may be appreciated that a need has arisen for atransmission system that provides multirate operation. In accordancewith the present invention, a multi-rate transmission system is providedthat substantially eliminates or reduces disadvantages and problemsassociated with conventional fixed rate transmission systems.

According to an embodiment of the present invention, there is provided amulti-rate transmission system that includes a receiver capable ofreceiving a serial data stream. The serial data stream has a first clockrate. A clock recovery unit generates a first clock signal with thefirst clock rate in response to the serial data stream. A serial to dataconverter converts the serial data stream into a parallel format inresponse to the first clock signal. A frame recovery unit places theparallel format into a frame format. The frame recovery unit is capableof operating at any of a plurality of clock rates to include the firstclock rate. With the frame recovery unit operating at the first clockrate, the serial data stream is made up of a plurality of consecutiveunique bits. With the frame recovery unit operating at a second clockrate that is an integer value fraction of the first clock rate, theserial data stream is made up of unique bits wherein each unique bitoccupies a number of consecutive bit positions equal to the integervalue in order to provide multi-rate operation.

The present invention provides various technical advantages overconventional fixed rate transmission systems. For example, themulti-rate transmission system can operate with any of a plurality ofclock rates. Another technical advantage is that unique bits can berepeated to adjust for differences in clock rates between systemcomponents. Yet another technical advantage is the ability to remotelychange the operating clock rate without swapping out system components.Other technical advantages are readily apparent to one skilled in theart from the following figures, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, wherein likereference numerals represent like parts, in which:

FIG. 1 illustrates a simplified block diagram of a multi-ratetransmission system;

FIG. 2 illustrates a bit sequence of a receive side of the multi-ratetransmission system at a first clock rate;

FIG. 3 illustrates a bit sequence of the receive side of the multi-ratetransmission system at a second clock rate; and

FIG. 4 illustrates a bit sequence of a transmit side of the multi-ratetransmission system at the second clock rate.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified block diagram of a multi-rate transmission system10. Multi-rate transmission system 10 includes a receive section 12 anda transmit section 14. Receive section 12 includes a receiver 16, aclock recovery unit 18, and a serial to parallel converter 20 operatingat a first clock rate M. Receiver section 12 also has a frame recoveryunit 22 operating at any one of a plurality of clock rates, includingfirst clock rate M and a second clock rate M/n. Transmitter section 14includes a transmitter 24, an oscillator 26, and a parallel to serialconverter 28 operating at first clock rate M. Transmitter 14 also has aframe formatter 30 operating at any one of a plurality of clock rates,including first clock rate M and second clock rate M/n.

In operation, a serial data stream is provided to receiver 16 ofreceiver section 12 from a transmission medium 32. Transmission medium32 may be any conventional carrier of telecommunications information toinclude a fiber optic communication path. Clock recovery unit 18generates a receive clock signal having first clock rate M in responseto the serial data stream received by receiver 16. Serial to parallelconverter 20 converts the serial data stream into a parallel format inresponse to the receive clock signal generated by clock recovery unit18. Frame recovery unit 22 identifies the frame information transferredby the serial data stream for further processing by telecommunicationcomponents in communication with receiver section 12.

FIG. 2 shows a bit sequence of the serial data stream for frame recoveryunit 22 operating at first clock rate M. Each bit position of the serialdata stream has a unique bit associated therewith at each clock pulse ofthe frame information transported from transmission medium 32. Framerecovery unit 22 selects every bit position of the received data inorder to properly interpret the data for appropriate processing.

FIG. 3 shows a bit sequence of the serial data stream for frame recoveryunit 22 operating at second clock rate M/n, where n is equal to 4. Eachunique bit of the frame information occupies a number of bit positionscorresponding to first clock rate M associated with an integer valueratio between first clock rate M and second clock rate M/n. For theexample shown, each unique bit of the frame information occupies fourbit positions of first clock rate M. Frame recovery unit 22 receivesdata at first clock rate M with each unique bit spanning four clockpulses of first clock rate M. Frame recovery unit 22 continues tooperate at first clock rate M, but selects every fourth bit position ofthe received data in order to correctly interpret the data. Framerecovery unit 22 arbitrarily selects the every fourth bit positionsequence. Though frame recovery unit 22 does not know where theboundaries are for each bit position, arbitrary selection will result inrecovery of a valid bit sequence.

For operation of transmit section 14, frame formatter 30 receivesunframed data from processing components in communication with transmitsection 14 and provides the appropriate overhead and data manipulationaccording to the clock rate desired for proper transmission of frameinformation. Frame formatter 30 generates a parallel format from theframe information that is converted into a serial data stream byparallel to serial converter 28. Oscillator 26 generates a transmitclock signal having first clock rate M to drive parallel to serialconverter 28. Transmitter 24 places the serial data stream ontotransmission medium 32 at first clock rate M.

For operation at first clock rate M, frame formatter 30 processes theframe information such that a unique bit is present at each bit positionof the serial data stream for each clock pulse of first clock rate M asshown in FIG. 2.

FIG. 4 shows a bit sequence of the serial data stream for frameformatter 30 operating at second clock rate M/n, where n is equal to 4.Each unique bit of the frame information is repeated a number of timesassociated with the integer value ratio between first clock rate M andsecond clock rate M/n. For the example shown, four repeats of eachunique bit of the frame information are performed by frame formatter 30.This allows for frame formatter 30 to provide data on transmissionmedium 32 at the slower second clock rate M/n through the components oftransmit section 14 operate at the faster first clock rate M.

Frame information can be transported at a maximum clock rate or at anyinteger value fraction of the maximum clock rate in thetelecommunications environment. The clock rate for multi-ratetransmission system 10 can be changed through software modificationswithout replacing all the components of multi-rate transmission system10.

In summary, a multi-rate transmission system can operate at a pluralityof rates by having the majority of components operating at a fixed firstclock rate and a single multi-rate component on both the receive andtransmit side operating at any of a plurality of clock rates. Uniquebits occupy each bit position of a serial data stream when allcomponents operate at the first clock rate. Unique bits are repeatedinto a number of bit positions in the serial data stream when the singlemulti-rate component of both the receive and transmit side operates at asecond clock rate which is an integer fraction of the fixed first clockrate.

Thus, it is apparent that there has been provided in accordance with thepresent invention, a multi-rate transmission system that satisfies theadvantages set forth above. Although the present invention has beendescribed in detail, it should be understood that various changes,substitutions, and alterations readily ascertainable to one skilled inthe art can be made herein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A multi-rate transmission system, comprising:areceiver operable to receive a serial data stream, the serial datastream having a first clock rate; a clock recovery unit operable togenerate a first clock signal in response to the serial data stream, thefirst clock signal having the first clock rate; a serial to parallelconverter operable to convert the serial data stream into a parallelformat in response to only the first clock signal; a frame recovery unitoperable to recover frame information from the parallel format, theframe recovery unit operating at only one of a plurality of second clockrates.
 2. The multi-rate transmission system of claim 1, wherein thesecond clock rate is identical to the first clock rate, the serial datastream being comprised of unique bits at each clock pulse of the firstclock rate.
 3. The multi-rate transmission system of claim 1, whereinthe second clock rate is an integer value fraction of the first clockrate.
 4. The multi-rate transmission system of claim 3, wherein theserial data stream has a plurality of unique bits, each unique bit beingrepeated in a number of consecutive bit positions, wherein the numberequals the integer value.
 5. The multi-rate transmission system of claim4, wherein the frame recovery unit selects every nth bit of the serialdata stream according to the second clock rate.
 6. A multi-ratetransmission system, comprising:a clock oscillator operable to generatea clock signal at a first clock rate; a frame formatter operable togenerate frame information into a parallel format in response to receiptof unframed data, the frame formatter operating at one of a plurality ofsecond clock rates the frame formatter generating repeated frameinformation in response to a difference between the first clock rate andthe second clock rate; a parallel to serial converter operable toconvert the parallel format into a serial data stream, the parallel toserial converter operating at only the first clock rate generated by theclock oscillator; a transmitter operable to send the serial data stream,the transmitter operating at the first clock rate.
 7. The multi-ratetransmission system of claim 6, wherein the second clock rate isidentical to the first clock rate, each bit position of the frameinformation having a unique bit corresponding to a clock pulse of thefirst clock rate.
 8. The multi-rate transmission system of claim 6,wherein the second clock rate is an integer value fraction of the firstclock rate.
 9. The multi-rate transmission system of claim 8, whereinthe frame information has a plurality of unique bits, the frameformatter repeating each unique bit a number of times equal to theinteger value.
 10. The multi-rate transmission system of claim 9,wherein the serial data stream includes the plurality of unique bits,each unique bit occupying consecutive bit positions of the serial datastream according to the integer value.